In typical OCT and OFDR systems, the spatial resolution of the measurement is determined by the range of a continuous sweep of a tunable laser source. Therefore, the measurement time of an OCT or OFDR system is limited by how quickly the laser can scan the wide wavelength ranges—for example, 100 nm at a rate of 100 kHz. The spatial resolution of the measurement is also limited by the technical limit of how wide a wavelength range that a single laser can scan. The current, single state-of-the-art tunable lasers operating at 1310 nm or 1550 nm can scan, at most, a 40-60 nanometer (nm) range. In applications that require a continuous, monotonic sweep of wavelength versus time, there is a desire to avoid substantial gaps in time during the sweep, since these gaps can create problems for the measuring instrumentation and slow the sweep.